The present invention relates generally to an information processing apparatus comprising a main storage and an extended storage, and more particularly to an information processing apparatus which is suitable for drastically improving a data move capability between a main storage and an extended storage.
A general purpose information processing apparatus is typically composed of a central processing unit (hereinafter abbreviated as "CPU"), a main storage (hereinafter abbreviated as "MS"), an input/output processing unit (hereinafter abbreviated as "IOP"), input/output devices connected to the IOP, and so on.
An input/output data processing procedure in the information processing apparatus composed of the units mentioned above is generally executed in the following manner. First, the IOP transfers input data from input/output devices connected to the IOP to the MS for temporarily storing the input data in the MS, and the data stored in the MS is processed by the CPU and again stored in the MS after the processing is completed. The processed data stored in the MS is then outputted to input/output devices through the IOP as output data.
The sequence of operations in the foregoing input/output data processing procedure is generally executed under the control of an operating system (hereinafter abbreviated as "OS") resident on the information processing apparatus. In addition, an approach for providing the OS with a virtual storage function is generally employed for apparently eliminating a limit to the capacity of the MS.
When the virtual storage function is included in an OS, a virtual storage device uses a storage capacity significantly larger than a real storage capacity of a MS. Thus, a portion of input/output devices connected to an IOP is generally used as an external storage device serving as a storage medium for the virtual storage device, such that data overflowing the actual storage capacity of the MS is temporarily stored in the external storage device. In this event, a data move operation, i.e., so-called page-in/page-out operations are executed by the MS and the external storage device under the control of the OS. Since the page-in/page-out operations are extremely frequently executed, the data move capability between the MS and the external storage device is a critical factor for determining the information processing performance of the information processing apparatus.
In recent years, it is a general tendency to employ an additional storage device called an "extended storage" (hereinafter abbreviated as "ES") which plays a different role from the MS and the external storage device for improving the data move capability in the page-in/page-out operations. The ES is a storage device dedicated to store, under the control of the OS, a portion or all of page data sets (data blocks) conventionally adapted to temporarily store data overflowing a real storage capacity of a MS using an external storage device connected to the IOP. The data move capability between the MS and the ES associated with page-in/page-out operations is quite higher as compared with the data move capability between the MS and an external storage device, since the former can move data without the intervention of an input/output interface. An increased data move capability between the MS and the ES associated with the page-in/page-out operations results in remarkable improvements in the information processing performance of the information processing apparatus.
U.S. Pat. Nos. 3,723,976; 4,761,737; 4,075,694; 4,685,057; and 5,371,867 disclose general services and functions of ES's in information processing apparatuses.
It should be noted that a page-in operation involving actual data transfer from an ES to a MS and a page-out operation involving actual data transfer from a MS to an ES are extremely frequently executed during the progress of data processing, so that the data transfer capability between the ES and the MS largely affects the data processing performance of the information processing apparatus.